1. Field of the Invention
The present invention relates to an electromagnet device and, more particularly, to an electromagnet device which is assembled in, for example, an electromagnetic relay.
2. Description of the Prior Art
The electromagnet device assembled in the electromagnetic relay is used to move the movable contact member of the electromagnetic relay between the ON position and the OFF position. At the ON position, the movable contact attached to the movable contact member come into contact with a fixed contact. At the OFF position, the movable contact is removed from the fixed contact. To drive the movable contact member, the electromagnet device has a pivotably movable assembly. The swing motion of the movable assembly is transferred to the movable contact. The movable assembly is moved by the attractive force and the repulsive force of the electromagnet. The movable assemble assembly comprises: two magnetic plates (iron plates) arranged so as to face each other with an interval; a supporting member, disposed between those two magnetic plates, for swingably supporting the magnetic plates at almost the central positions in their longitudinal directions; and two permanent magnets arranged at the positions on both sides of the supporting member so as to be sandwiched between the two magnetic plates. On the other hand, a substantially C-shaped core is provided. A coil is wound around a part of the core. Each end of the core is inserted between the end portions of the two magnetic plates so as not to come into contact with those end portions of the magnetic plates. The movable assembly is driven so as to swing around the supporting member as a center by the attractive or repulsive force between the magnetic poles which are developed at both ends of the core in dependence on the direction of a current flowing through the coil and the magnetic poles which are generated in the magnetic plates by the permanent magnets.
According to such a conventional electromagnet device, the magnetic efficiency is high because the attractive or repulsive forces act at four positions in the movable assembly. However, since two permanent magnets are necessary to form magnetic circuits, there is such a problem that the device increases in size. In addition, since each end portion of the core is disposed so as to be sandwiched between the two magnetic plates in the contactless state, if the end portions of the core are moved to approach (or removed from) one of the two magnetic plates in order to adjust the magnitude of the attractive or repulsive force which acts only between one magnetic plate and the core, the distance between end portions of the core and the other magnetic plate increases (or decreases), so that the attractive or repulsive force which acts between the core and the other magnetic plate also changes. Consequently, it is impossible to perform such an adjustment.